1. Field of the Invention
The present invention relates to a video storage and delivery apparatus and a video storage and delivery system, which are particularly suitable for supplying video data to a plurality of clients at the same time.
2. Description of the Related Art
FIG. 26A shows a conventional example of an information processing apparatus. The apparatus includes a central processing unit (CPU) 2610, a memory 2620, and input/output (I/O) units 2670. The CPU 2610 is connected to the memory 2620 by a system bus 2601. There is additionally provided an I/O bus 2602 to be linked with the system bus 2601 via a bus interface (I/F) 2603. Moreover, the information processing apparatus is coupled with, for example, a data storage device 2660 and/or a network 2650 via the output units 2670 disposed in I/O control blocks 2640 and 2641, respectively.
FIG. 26B shows another example of the information processing apparatus. This apparatus is configured in a similar manner as for the apparatus shown in FIG. 26A. In this construction, however, a plurality of CPUs 2610 and a plurality of I/O units 2670 are connected to the system bus 2670 to concurrently operate the plural cPUs 2610 for an improved processing performance (in a tightly coupled multiprocessor configuration).
In addition, an information processing system is configured by interconnecting a plurality of workstations (WSs) and/or personal computers (PCs) to each other via a local area network (LAN). For the network, there can be used, for example, the Ethernet having a throughput of approximately eight megabits per second (Mbps) and the fiber distributed data interface (FDDI) having a throughput of approximately 100 Mbps.
Recently, the asynchronous transfer mode (ATM) has been put to use for the LAN. The ATM-LAN differs from the communication method of the Ethernet and FDDI in which a communication line is used in a timesharing fashion. Namely, according to the ATM-LAN, a plurality of communication channels can be established through an ATM switch, which improves the throughput of the overall communication system. Each information processing apparatus has an interface provided with a plurality of hierarchically arranged throughput levels including, for example, approximately 50 Mbps, 150 Mbps, and 600 Mbps, respectively. Data items at lower-levels are collected by the multiplexer to be connected to a higher hierarchic level.
According to an increase in the transmission speed of communication lines, there arises a need for communication of a large volume of video data via a network. Using video data, it is possible to supply the users with various kinds of information items, which cannot be transferred by text data. Furthermore, to decrease the memory capacity and transmission bands, there are available such data compression functions as "JPEG", "MPEG", and "H.261".
An attempt has been made to develop a software system in which compressed video data (approximately 1.2 Mbps) is simultaneously delivered via the Ethernet to a plurality of clients, namely, about 20 clients terminals. As a data storage apparatus to store therein a large amount of data, there has been devised a redundant array of inexpensive disks (RAID). In this apparatus, a plurality of disk devices are connected to each other in a parallel manner for simultaneous operations thereof such that data items are stored on the respective disks in a striping fashion so as to improve the data access throughput. Moreover, information items such as parity bits are stored beforehand on redundant disks such that even when there appears a defective data block, it is possible to restore the correct original data.
There has been also implemented a data storage apparatus called an optical disk jukebox having a large capacity. The apparatus includes a plurality of optical disks such that an arbitrary optical disk can be selected for data output operation.
To supply time-series video data items to a plurality of users at the same time or in a concurrent fashion, there are required a large-capacity data storage apparatus capable of achieving reading and writing operations at a high speed and a network capable of transmitting data of a large capacity at a high transfer speed. When data storage apparatuses of this type are connected to each other via a conventional bus, there occurs a problem of data concentration of the bus.
In addition, video data is different from ordinary text data to be treated by the information processing apparatus. Namely, the video data is required to be controlled with respect to a time axis. In other words, it is necessary to guarantee quality of service (QOS) by constantly supplying each user terminal with video data having a quantity (per second) associated with the terminal so that an appropriate image is obtained by a display thereof.
To conduct delivery service of video data, when the information processing system has a configuration including the conventional bus, that is, when the plural file devices to store therein video data items (or a plurality of video storage and delivery apparatuses respectively having video file devices) are connected via a bus to a network, there occurs conflict between request issued from a plurality of units for the right to use the bus. As a result, a unit granted the right is given the right to transmit video data, which consequently makes is possible to guarantee the quality of service.